Somatic cell hybridization will be used to investigate the genetic basis of growth characteristics associated with malignancy, e.g., transplantability, and growth on methylcellulose or soft agar. The genetic basis of thermostability at elevated temperatures will be studied in the same way, by karyotypic analysis using chromosome banding methods. Additional, more specific banding techniques will be developed, to enhance the accuracy of identification of karyotypic changes. BIBLIOGRAPHIC REFERENCES: Miller, O.J., Miller, D.A., Dev, V.G., Tantravahi, R. and Croce, C.M.: Expression of human and suppression of mouse nucleolus organizer activity on mouse-human somatic cell hybrids. Proc. Natl. Acad. Sci. U.S.A. 73: 4531-4535, 1976. Croce, C.M., Talavera, A., Basilico, C. and Miller, O.J.: Suppression of the production of mouse 28S ribosomal RNA in mouse-human hybrids segregating mouse chromosomes. Proc. Natl. Acad. Sci. U.S.A. 74: 694-697, 1977.